Temporal analysis of stochastic turning behavior of swimming C. elegans.

Caenorhabditis elegans exhibits spontaneous motility in isotropic environments, characterized by periods of forward movements punctuated at random by turning movements. Here, we study the statistics of turning movements-deep Omega-shaped bends-exhibited by swimming worms. We show that the durations of intervals between successive Omega-turns are uncorrelated with one another and are effectively selected from a probability distribution resembling the sum of two exponentials. The worm initially exhibits frequent Omega-turns on being placed in liquid, and the mean rate of Omega-turns lessens over time. The statistics of Omega-turns is consistent with a phenomenological model involving two behavioral states governed by Poisson kinetics: a "slow" state generates Omega-turns with a low probability per unit time; a "fast" state generates Omega-turns with a high probability per unit time; and the worm randomly transitions between these slow and fast states. Our findings suggest that the statistics of spontaneous Omega-turns exhibited by swimming worms may be described using a small number of parameters, consistent with a two-state phenomenological model for the mechanisms that spontaneously generate Omega-turns.